Physico-Chemical Properties of Silk Sericin Extracted by Hydrothermal Treatment

In this work, studies were conducted to achieve the complete extraction of sericin from natural silk cocoons at temperatures of 100 °C and 110 °C for durations ranging 2–24 h without the use of chemical reagents. As a result, sericin samples with molecular weight changing 20–240 kDa were obtained. During the thermal and sublimation drying of the isolated sericin samples, changes in their solubility were observed. Structural changes in the thermally dried sericin samples were analyzed using X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy. XRD analysis revealed diffraction peaks at 18.9° and 20.7°, indicating the presence of crystalline structure, whereas the samples dried by sublimation exhibited a completely amorphous structure. FTIR spectroscopy showed band broadening in the regions of 3000–3500 cm^− 1 and 1500–1600 cm^− 1 in the thermally dried samples, which was attributed to extensive hydrogen-bond formation compared to the samples dried by sublimation. Rheological analysis further demonstrated that the loss modulus exceeded the storage modulus for sericin sample. The results demonstrate that extract sericin under high temperature without chemical reagent enables the efficient isolation of sericin with different molecular weight, while the drying method strongly influences its structural, solubility, and rheological properties.